In recent years, the HDMI has prevailed as a communication interface via which a digital video signal, that is, an uncompressed (baseband) video signal (hereinafter, referred to as image data), and a digital audio signal accompanying the video signal (hereinafter, referred to as audio data) are transmitted at a high speed from, for example, a digital versatile disc (DVD) recorder, a set-top box, or any other audiovisual (AV) source to a television set, a projector, or any other display (refer to, for example, patent document 1).
As for the HDMI, a transition minimized differential signaling (TMDS) channel on which the image data and audio data are transmitted unidirectionally from an HDMI source to an HDMI sink at a high speed, and a consumer electronics control line (CEC line) over which bidirectional communication is performed between the HDMI source and HDMI sink are stipulated.
FIG. 21 shows an example of the configuration of a conventional communication system 200. The communication system 200 includes source equipment 210 and sink equipment 220. The source equipment 210 and sink equipment 220 are connected to each other over an HDMI cable 230.
The source equipment 210 includes a control unit 211, a reproduction unit 212, an HDMI transmitting unit (HDMI source) 213, a power circuit 214, and an HDMI terminal 215. The control unit 211 controls the actions of the reproduction unit 212 and HDMI transmitting unit 213 respectively. The reproduction unit 212 reproduces baseband image data (uncompressed video signal) of a predetermined content and audio data (audio signal) accompanying the image data from a recording medium that is not shown, and feeds the data items to the HDMI transmitting unit 213. Selection of a reproductive content in the reproduction unit 212 is controlled by the control unit 211 on the basis of a user's manipulation.
The HDMI transmitting unit (HDMI source) 213 unidirectionally transmits baseband image data and audio data, which are fed from the reproduction unit 212, to the sink equipment 220 through the HDMI terminal 215 over the HDMI cable 230 by performing communication conformable to the HDMI. The power circuit 214 feeds power to the internal circuits of the source equipment 210, and feeds power to the sink equipment 220 through the HDMI terminal 215 over the HDMI cable 230.
The sink equipment 220 includes an HDMI terminal 221, a control unit 222, a memory unit 223, an HDMI receiving unit (HDMI sink) 224, and a display unit 225. The control unit 223 controls the actions of the HDMI receiving unit 224 and display unit 225 respectively. The memory unit 223 is connected to the control unit 222. In the memory unit 223, an enhanced extended display identification (E-EDID) and other information necessary to control for the control unit 222 are stored.
The HDMI receiving unit (HDMI sink) 224 receives baseband image data and audio data that are fed to the HDMI terminal 221 over the HDMI cable 230 through communication conformable to the HDMI. The HDMI receiving unit 224 feeds the received image data to the display unit 225. The HDMI receiving unit 224 also feeds the received audio data to, for example, a loudspeaker that is not shown.
A 18 pin of the HDMI terminal 215 of the source equipment 210 and a 18 pin of the HDMI terminal 221 of the sink equipment 220 are power terminals. Therefore, when the HDMI terminals 215 and 221 are connected to each other over the HDMI cable 230, power from the power supply 214 of the source equipment 210 is fed to the sink equipment 220 by way of the pin 18 of the HDMI terminal 215, the HDMI cable 230, and the 18 pin of the HDMI terminal 221.
A 19 pin of the HDMI terminal 215 of the source equipment 210 and a 19 pin of the HDMI terminal 221 of the sink equipment 220 are Hot Plug Detect (HPD) terminals. The 19 pin of the HDMI terminal 221 is connected to a +5 V power supply via a resistor of 1 kΩ. The voltage at the 19 pin of the HDMI terminal 215 is monitored by the control unit 211. Therefore, when the HDMI terminals 215 and 221 are connected to each other over the HDMI cable 230, the voltage at the 19 pin of the HDMI terminal 215 is raised. Eventually, the control unit 211 recognizes that the sink equipment 220 has been connected to the source equipment 210 over the HDMI cable 230, and initiates a predetermined action.
The operation of the communication system 200 shown in FIG. 21 will be described below. Based on a user's selecting manipulation, the reproduction unit 212 of the source equipment 210 reproduces a predetermined content. Baseband (uncompressed) image data and audio data relevant to the predetermined content obtained by the reproduction unit 212 are fed to the HDMI transmitting unit (HDMI source) 213. The HDMI transmitting unit 213 unidirectionally transmits the baseband image data and audio data to the sink equipment 220 over the HDMI cable 230 through communication conformable to the HDMI.
The HDMI receiving unit (HDMI sink) 224 of the sink equipment 220 receives the baseband image data and audio data, which are unidirectionally transmitted over the HDMI cable 230, from the source equipment 210 through communication conformable to the HDMI. The baseband (uncompressed) image data received by the HDMI receiving unit 224 is fed to the display unit 225. In the display unit 225, the image data fed from the HDMI receiving unit 224 is processed and an image represented by the image data is displayed. The baseband (uncompressed) audio data received by the HDMI receiving unit 224 is fed to a loudspeaker that is not shown, and sounds represented by the audio data are outputted.
The patent document 1 refers to JP-A-2006-319503.